1. Field of the Invention
The present invention relates to an electromechanical transducer and a fabrication method of an electromechanical transducing apparatus.
2. Description of the Related Art
Recently, research pertaining to electromechanical transducers using micromachining has been widely conducted. Particularly, a capacity-type of electromechanical transducer is a device to transmit or receive elastic waves such as ultrasonic waves using a lightweight vibrating film, and a wide bandwidth is readily obtained whether in liquid or in air, thereby has received focus as a technique more desirable for high-precision ultrasound wave diagnosis than current medical diagnostic modality.
Such a capacity-type electromechanical transducer is made up of elements wherein multiple cells having a space (hereafter called cavity) between a substrate and a thin film which is a vibrating membrane are formed and electrically connected. An electromechanical transducing apparatus is created by electrically bonding an integrated circuit to a substrate serving as the electromechanical transducer. However, since the substrate itself is thin, there has been the problem of easily breaking during handling or processing at the time of fabrication. Also, the substrate detects a signal for each element, and therefore may perform trench formation to form a recessed portion by removing a portion of the back face of the face whereupon the vibrating membrane is formed by shaving, polishing, etching, and so forth. By performing such trench formation, lower electrodes can be separated by element, and a signal can be detected for each element. However, the substrate has a thin substrate itself, which the trench formation causes to be thinner still, whereby performing further back-face processing with the substrate alone becomes difficult.
Now, Sensors and Actuators A 138 (2007) 221-229 described a technique wherein, in order to protect the vibrating membrane and to strengthen the substrate itself, a quartz substrate is used as a handling member, which is fixed to a face on the vibrating membrane side of the substrate, via a dry film. Subsequently, trench formation and fabrication of a lower electrode is performed on the back face of the fixed face, and flip chip bonding is used to bond with the integrated circuit. Lastly, the quartz substrate using for handling is removed and the cell surface is exposed to fabricate the electromechanical transducing apparatus.
Also, Japanese Patent Laid-Open No. 2007-188967 discloses a substrate processing method which, although differing from the electromechanical transducer, provides a channel to the handling member and supports the substrate, and performs back-face processing and the like of the substrate. By forming a metallic layer on the channel of the handling member, in the event that the handling member is removed, an acid or alkali dissolving solution to dissolve metal is supplied to the channel, whereby the handling member is separated from the substrate.